Unable to join two nodes in Compositor
You are not supposed to plug a composite node into the denoise node- or any other node for that matter.
The composite node represents the output the compositor will return. What you plug into it will be returned as the output.
To use the denoise node, you will instead need to hook it up to the render layers node. This is the output from the render result you have just generated. Plug &quot;Noisy Image&quot; into &quot;Image&quot;, &quot;Normal&quot; into &quot;Denoising Normal&quot;, and &quot;Denoising Albedo&quot; into &quot;Albedo&quot;. Now drag the output &quot;Image&quot; of the denoise node into the input &quot;image&quot; of the composite node.
The compositor is designed to change the render result, sort of like an image editor except it is node based and more powerful.